Inhalation is a very old method of drug delivery. In the twentieth century it became a mainstay of respiratory care and was known as aerosol therapy. Use of inhaled epinephrine for relief of asthma was reported as early as 1929, in England. Dry powder inhalers have been utilized to administer penicillin dust to treat respiratory infections. In 1956, the first metered dosed inhaler was approved for clinical use.
The scientific basis for aerosol therapy developed relatively late, following the 1974 Sugar Loaf conference on the scientific basis of respiratory therapy.
A more complete history of the development of aerosol therapy and the modern nebulizer is described in the 2004 Phillip Kitridge Memorial Lecture entitled, “The Inhalation of Drugs: Advantages and Problems by Joseph L. Row; printed in the March 2005 issue of Respiratory Care, vol. 50, no. 3.
The typically used modern nebulizer is delivered as a kit of seven plastic pieces, which are assembled prior to use to provide for delivery of the medication to a patient via inhalation. An exploded view of the seven pieces showing their relationship for assembly is given in FIG. 1. There is a mouthpiece 100 that is force fit onto one end of a T connector 110. Similarly, the other end of the T connector 110 is attached to a flex tube 120, also by force fit. The parts are such that the components can be assembled and disassembled with a simple twisting action. Nevertheless, when engaged and pressed together, the pieces form a substantially airtight seal. The bottom part of the T connector 110 is connected to a cup cover 130. That, too, is connected by pushing the cup cover onto the bottom part of the T connector in such a way that the airtight seal is formed. The cup cover 130 has a screen 135 that screens the material going into the T connector. There is a cup 150 for receiving the medicine to be nebulized. The cup also has a venturi projecting through the bottom.
In a typical use, a vial containing the medication for administration through the nebulizer is opened and poured into the cup 150 where it accumulates at the edges of the rounded bottom of the cup. The venturi is surrounded by a conical plastic piece through which it passes. The shape of the conical piece of the medicine cup 150 matches substantially the shape of the venturi cover 140. Once the medicine is poured into the cup, the venturi cover 140 is placed over the venturi and the filled medicine cup is screwed, using threaded portions on each piece, onto the cup cover 130. In this way, the medicine is held in place ready for administration.
In use, the bottom of the airline feeding the venturi in the medicine cup is attached to an air hose 160, to which is applied to a source of air pressure thus activating air flow through the venturi. By venturi action, the exhaust of the air flow through the small opening of the venturi results in a reduction in pressure on the downstream side of the air flow so that the medicine from the medicine cup is fed under positive pressure up in the interstices between the conical shape of the medicine cup and the venturi cover and is exhausted then through the screen 135 into the bottom of the T connector 110.
A patient is asked to inhale the aerosol mist provided through the cup cover screen into the air flow channel between the mouthpiece 100 and the flex tube 120. As a patient takes the mouthpiece 100 in their mouth, and inhales, air flows through the open end of the flex tube 120, through the T connector 110, picking up the aerosol medication and into the patients' air passages through the mouthpiece 100.
Table 8 of the Respiratory Care article, referred to above, page 381, lists the characteristics of an ideal aerosol inhaler as follows:
TABLE 8Dose reliability and reproducibilityHigh lung-deposition efficiency (target lung depositionof 100% of nominal dose)Production of the fine particles ≦5 μm diameter, withcorrespondingly low mass median diameterSimple to use and handleShort treatment timeSmall size and easy to carryMultiple-dose capabilityResistance to bacterial contaminationDurableCost-effectiveNo drug released to ambient-airEfficient (small particle size, high lung deposition)for the specific drug being aerosolizedLiked by patients and health care personnel
The standard nebulizer shown in FIG. 1, fails to achieve a number of these characteristics. Specifically, the nebulizer of FIG. 1 wastes medication during exhalation. Further, the particle size is often too large to reach the bottom of the lungs where the medication may be most needed. There is difficulty in estimating the dose of the drug being given to a patient and there is difficulty in reproducing that dose. There is a possibility of contamination when opening the initially sterile kit, poring medication into the cup, and assembling the pieces for use by a patient. There is also considerable inefficiency in the medication delivery, with much of it being deposited in the throat, rather than in the lungs.
Commonly assigned U.S. Patent Publication Nos. 2007/0163572 and 2007/0107725, and which are identified above as the incorporated by reference '993 and '689 applications, disclose intra-oral nebulizers in which the nebulizer places a venturi in close proximity to or inside a patient's oral cavity. One or more feed lines feed the medicine to a location proximate to a venturi. Medicines can be administered simultaneously to a patient. Air pressure is applied to the venturi to aid in nebulization.
When a patient performs a treatment with the nebulizer, it would be advantageous to determine if the patient's respiratory function has improved due to the use of the drug being administered. Also, it would be advantageous for the patient to use the nebulizer for respiratory exercise and incentive spirometry uses in which flow and pressure can be measured over time and pulmonary function testing performed.